Fuse construction



April 16, 1957 L. N. BAENZIG ER FUSE CONSTRUCTION Filed April 18, 1955 United States Patent O FUSE CONSTRUCTION Leonard N. Baenziger, Pawtucket, R. assignor," by mesne assignments, to Royal Electric Corporation, Pawtucket, R. I., a corporation of Delaware Application April 18, 1955, Serial No. 501,869

16 Claims. (Cl. Nil- 123) The present invention relates to a novel construction for a circuit protective fuse. The type of fuse to which this invention particularly relates is one which is adapted not only immediately to protect the circuit in which it is connected from extreme current overloads, such as might be caused by a short circuit or the like, but also to protect the circuit against minor overloads which persist beyond a predetermined period of time.

Fuses of this particular type generally comprise a conductive link formed of readily fusible material, the link itself therefore being self-destructive so as to open the circuit through the fuse quite promptly upon the occurrence of heavy overloads. A portion of the electrical circuit through the fuse is additionally defined by a material having a fairly low melting point, that material serving to physically and electrically connect two elements together and being held under tension in juxtaposition to a current carrying element having an appreciable electrical resistance. Slight overloads will cause the element of high electrical resistance to heat up sufficiently to melt or soften the connecting material, and because of the tension thereon the junction defined thereby will separate provided that the heating eifect of the high resistive element continues at a sufficient magnitude for a sutiicient period of time. In this manner if a slight overload should occur the circuit through the fuse will not be immediately opened, but if that slight overload should continue for an excessive period of time, the circuit will be opened. The period of time will of course vary depending upon the magnitude of the overload, the greater the current the greater the heat developed in the element having a high electrical resistance, and consequently the sooner will the junction material be softened or melted.

The fuse structure of the present invention provides for a simplified yet positively acting arrangement of parts in a device of this character. In particular it eliminates the necessity for providing a heating element having a high electrical resistance separate and independent from the other elements of the fuse. To this end the high resistance heating element is constituted by one of the external teminals of the fuse, preferably the central terminal at the bottom thereof. The link formed of fusible material and adapted to melt upon the passage through the fuse of an excessive overload is directly secured to this high resistive terminal by means of a low melting point solder, the solder being applied over a substantial area of the terminal so as to be effectively heated thereby. That portion of the link connected to said terminal is maintained under tension by means of a spring, and the tensioned portion of the link is weakened at one or more points so as to melt at those points when an excessive overload exists, the spring therefore serving to positively and quickly open the circuit through the fuse upon the existence either of an excessive overload or a slight overload which persists for an excessive period of time.

The structure of the present invention further has reference to an improved operative connection between the spring and the tensioned part of the link. To that end "ice a pin is passed through the link at a point remote from the terminal of high resistivity, and the spring 1s operatively connected between the housing and the pin. The passage of the pin through the link itself produces a weakened area of the link which will tend to fuse or melt upon the existence of an excessive overload, the action of the spring on the pin, and through the pin on the link itself, serving to cause the link to separate quickly in the event such fusing or melting takes place. The operative springlink interconnection also simplifies the internal electric circuitry of the fuse, as well as its mechanical construction, and serves effectively to insulate the spring, which usually is formed of metallic and hence conductive material, from the link.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to a fuse construction as defined in the appended claims and as described in this specification, taken together with the accompanying drawings, in which:

Fig. 1 is a cross sectional view of a fuse made according to the present invention and showing the fuse in normal condition;

Fig. 2 is a partial cross sectional view thereof taken along the line 2-2 of Fig. l;

Fig. 3 is a view similar to Fig. l and showing the manner in which the circuit through the fuse is broken in the event of an excessive overload; and

Fig. 4 is a view similar to Fig. 3 but showing the manner in which the circuit through the fuse is broken in the event that a moderate overload persists for an excessive period of time.

The fuse comprises a base plug 2 formed of a suitable insulative heat resistive material such as a ceramic Or synthetic plastic and a body generally designated 4 also formed of an insulative material such as glass. The base plug 2 is provided with a flange 6 from which a sleeve 3 extends upwardly, the lower portion of the base 2 being tapered and terminating in a bottom surface 10 Within which a recess 12 is formed, the recess 12 communicating with a passageway 14 which leads into the space 16 inside the sleeve 8. The body 4 has a depending annular skirt 18 adapted to rest on the upper surface 20 of the flange 6, a bead 22 being formed on the outer surface thereof so as to dene a screw thread. A correspondingly threaded shell 24 of conductive material engages with the bead 22 and is provided with a lower inwardly extending lip 26 which engages the undersurface 28 of the base flange 6, thus holding the base 2 and the body 4 in assembled condition. The shell 24 defines one of the exposed terminals of the fuse and also constitutes the means by which the fuse may be screwed into the socket adapted to receive it.

The other external terminal of the fuse, located as is conventional in the lower tip thereof, is defined by a button 30 of material having an appreciable electrical resistance, that button being received in the base recess 12 and having a flange 32 integral therewith and projecting up therefrom through the passage 14, the upper end of the flange 32 being adapted to be spun over at 34 so as to rest upon an appropriately inclined inner surface of the base 2, thus serving to retain the button 3() in place. lt will be seen that the button 30 is of appreciable volume, and is considerably larger than is normally the case for conventional center fuse contacts.

The fusible link 36 is in the form of a exible strip of conductive material the composition of which is conventional and well known. One end 38 of the link 36 extends down between the base sleeve 8 and the body skirt 18, under the lower edge of the skirt 18 and up along the outer surface of the skirt 1S, the bead 22 being interrupted to permit the link end 38 to extend thereabove, the link end 38 then being electrically connected to the., shell 24 as by means of solder 40. The body of the link 36 extends into the open interior 42l of the body 4, and the other end 44 of the link 36 extends downwardly to the terminal button 3l), to which it is connectedtby means Vof, a massr of Soldierl r the like 46 having a comparatively low melting or softening point. This solder 46 is of a conventional type often used in fuses,'andk the various formulations of its composition are well known to those in the art.

Resting on the upper surface 480i the base sleeve 8 is an insulating washer Sil provided with an aperture 52; throughV which the link end. 44 is freely passable. A pin 54 passes through the link 36 and rests on the upper surface of the Washer 50. A spring 56, here shown as of the coiled compression type, is mounted between the undersurface of the washer t? and the bottom of the space 16 inside the base 2, the spring 56 tending to force the washer 50 upwardly, that upward biasing being transmitted to the link end 44 by means of the piny 4. Consequently that portion of the link end 44 beneath the pin4 54 is retained under tension, and the joint between the link end 44 andthe contact button 30 is also maintained under tension, the spring 56 constantly tending to withdraw the link end 44 from the solder 46. That solder 46, in its normal hardened condition, will resist such separation.

In order to provide an internal guide for the spring S6, and to ensure its electrical insulation from the link end 44, an insulating sleeve 58 is interposed between the spring 56 and the link end 44, that sleeve resting upon a lower surface of the space 16 within the base 2, and being here shown as resting directly upon the tip of the spun over portion 34 of the contact button ange 32.

It will be apparent that the cross section of the link 36 where the pin 54 passes therethrough is considerably less than over the remainder of the link 36. Consequently, if an excessive overload should occur, the link 36 will tend to fuse or melt in that area of reduced cross section, and that tendency will be accentuated by the fact that separative tension is applied to that very area. Consequently, as illustrated in Fig. 3, when the link 36 fuses at that area the spring 56, through the intermediation of the washer Sil and pin 54, will tend to separate the body of the link 36 from the lower end 44 thereof, thus snapping the link apart and positively and quickly opening the circuit through the fuse and therefore interrupting the passage of current therethrough.

Upon the occasion of a moderate overload, the current passing through the contact button 30, which has an appreciable electrical resistivity, will cause that button Si? to heat up above its normal condition. The extent of this heating eect will of course be dependent upon the magnitude of the current passing therethrough in accordance with conventional electrical laws. As the button 30 heats up the low melting point solder 46 thereon will be correspondingly heated, and eventually, if the overload persists long enough and is of sufcientt magnitude, the solder 46 will eventually be softened by heat to such a degree that, as may be seen from Fig. 4, the spring 56, acting through the intermediation of the washer 5t) and pin 54, will literally pull the tip of the link endV 44 up and out of the solder 46, thus opening the circuit through the fuse andV interrupting the passage of current therethrough. The size of the Contact button 30, which Yconstitutes a particularly massive circuit-carrying element, provides a considerable degree of thermal inertia, so that the fuse will not function to break the circuit upon the occurrence of slight overloads which are only of short duration. The duration of overload which will cause the circuit to be interrupted, which duration will of course be diiferent in the event of overloads of different magnitudes, can be controlled in the design of the fuse by varying the resistivity and the mass of the contact button 30, as well as by the composition of the low melting point solder 46.

It will be seen from the above that the construction in question isV extremely sturdy andv simple, that the fuse parts may be very readily assembled, and that the number of parts are minimized, particularly in view of the fact that the central contact itself constitutes the element of appreciable resistance adapted to heat and soften the low melting point solder 46.

While but a single embodiment of the present invention has been here disclosed, it will be apparent that many variations may be made therein, all within theV spirit of the present invention as defined in the following claims.

I claim:

l. A fuse construction comprising a hollow housing having first and second terminals exposed at the exterior thereof, said first terminal being located at the bottom of said housing, extending into said housing, and being formed of material having a comparatively high resistance, a fusible link inside said housing electrically between said terminals and connected to said first terminal by material having a low melting point, said link having an aperture therethrough in a part thereof above said first terminal, a pin passing through said aperture, and a spring active between said housing and said pin and urging said pin upward away from said first terminal, thereby maintaining the connection between said link and said iirst terminal under tension.

2. A fuse construction comprising a hollow housing having rst and second terminals exposed at the exterior thereof, said rst terminal being located at the bottom of said housing, extending into said housing, and being formed of material having a comparatively high resistance, a fusible link inside said housing electrically between said terminals and connected to said first terminal by material having a low melting point, said link having an aperture therethrough in a part thereof above said first terminal, a pin passing through said aperture, and a spring compressed between said housing and said pin and urging said pin upward away from said first terminal, thereby maintaining the connection between said link and said rst terminal under tension.

3. A fuse construction comprising a hollow housing having tirst and second terminals exposed at the exterior thereof, said rst terminal being located at the bottom of said housing, extending into said housing, and being formed of material having a comparatively high resistance and being of comparatively large volume, ya fusible link inside saidV housing electrically between `said terminals and connected to said iirst terminal by material having a low melting point, said link having an aperture therethrough in a part thereof above said lfirst terminal, `a pin passing through said aperture, and a `spring active between said housing and lsaid pin and urging said pin upward away from said first terminal, thereby maintaining the connection between said link and said rst terminal under tension.

4. A fuse construction comprising a hollow housing having first and second terminals exposed at the exterior thereof, said first terminal being located Iat the bottom of said housing, extending into said housing, and being formed of material having a comparatively high resistance and being of comparatively large volume, a fusible link inside said housing electrically between said terminals and connected to said -rst terminal by material having a low meltingy point, said link having an apenture .therethrough in a part thereof above said iirst terminal, a pin passing through said aperture, and `a spring compressed between said housing and said pin and urging said pin upward away `from said first tenminal, thereby maint-aining lthe connection between said link and said tirst terminal under tension.

5'. In the fuse construction of cla-im 2, a washer interposed between said pin and said spring.

6. In the fuse construction of claim 2, a sleeve surrounding a portion of said link below said pin and resting on the bottom of said housing, said spring surrounding said sleeve.

7. In the `Suse construction of claim 2, a sleeve surrounding `a portion of said link below s-aid pin and resting on the bottom of said housing, said spring surrounding said sleeve, iand la washer normally resting on top of said sleeve, said pin engaging the lupper surface of said washer and said spring engaging the lower surface thereof.

8. In the fuse construction of claim 4, a washer interposed between said pin and said spring.

9. In the `fuse construction of claim 4, a sleeve surrounding `a portion of said link below said pin and resting `on the bottom yof said housing, said spring surrounding said sleeve.

10. In the fuse construct-ion of claim 4, `a sleeve surrounding a portion of said link below said pin and resting on the bottom of said housing, said spring surrounding said sleeve, and a washer normally resting on top of said sleeve, said pin engaging the upper sur-face of said Washer and said spring engaging the lower surface thereof.

11. A lfuse construction comprising ya hollow housing having terminals exposed `at the exterior thereof, a fusible link inside said housing electrically between said terminals, an element in said housing to which said fusible link is connected by material having la low melting point, means in said housing and electrically between said terminals and supplying heat to said material, said link having an aperture therethrough in a part thereof spaced from said element, a pin passing through said aperture, and resilient 6 means lactive on said pin to urge it away from said element, thereby maintaining the connection between said link and said element under tension.

12. The fuse construction of claim ll, in which said element is located at the bottom of said housing, and in which said resilient means comprises a spring compressed between said housing `and said pin.

13. The -fuse construction of claim 1l, in which said resilient means comprises a spring compressed between said housing and said pin.

14. ln `the fuse construction of claim 13, a washer interposed between said pin and said spring.

15. In the fuse construction of cla-im 13, a sleeve surrounding a portion of said link between vsaid pin and said housing, said spring surrounding said sleeve.

16. in the yfuse construction of claim 13, a sleeve 4surrounding `a portion of said link between said pin and said housing, said spring surrounding said sleeve, and a washer normally resti-ng on top of said sleeve, said pin engaging the upper surface of said washer and said spring engaging the lower surface thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,693,404 Sandin Nov. 27, 1928 2,113,155 Kiefer Apr. 5, 1938 2,218,274 Wood Oct. 15, 1940 2,239,390 Jung et al Apr. 22, 1941 

